Geomagnetic induction studies in Scandinavia - I. Determination of the
inductive response function from the magnetometer array data
Alan G. Jones
Data from the Muenster IMS Magnetometer Array (Kueppers et al., 1979) have been analysed in the frequency domain to derive
the inductive response function, C(w,0), from the ratio of the vertical magnetic field to the spatial gradient of the
horizontal magnetic field.
The response function was best determined by statistical frequency analysis techniques after the spatial gradients had been
derived by least-squares fitting of two-dimensional, second-order polynomials to the observations, with the constraint imposed
that the solutions be curl-free.
The derived response function was found to obey two different causality requirements, and most of the inequality constraints imposed
on it (Weidelt, 1972).
A preliminary model, in which conductivity is a function of depth only and which explains the major details of the observed response,
It has a highly resistive uppermost layer of some 10,000 ohm.m, and of depth of the order of 30 km thick, underlain by a layer of about
125 ohm.m to a depth of around 140 km, where a transition takes place to a highly conducting half space (3 ohm.m).
The effect of various non-uniform sources on the observations of C(w,k) for this 1D model is illustrated.
Journal of Geophysics (Zeitschrift fuer Geophysik), 48, 181-194.
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Alan G Jones / 26 February 2010 /